The present invention relates to hydraulic control devices.
The invention is particularly concerned with a hydraulic control device to vary the displacement of a hydraulic piston unit, such as pump or motor. Control devices have been proposed for keeping the torque constant, and such a construction is, for example, illustrated in U.S. Pat. No. 3,510,231 and Swiss Patent Specification No. 469,908. The arrangement involves the use of three springs. Such constructions can only be set within a limited range of torques, unless the springs are changed. Furthermore, the torque must initially be set on a test stand and the construction of such a hydraulic unit is relatively expensive since the unit is rather bulky.